Encyclopedia of Espionage, Intelligence, and Security

Operation Magic

█ ADRIENNE WILMOTH LERNER

Operation Magic was the cryptonym given to United States efforts to break
Japanese military and diplomatic codes during World War II. The United
States Army Signals Intelligence Section (SIS) and the Navy Communication
Special Unit worked in tandem to monitor, intercept, decode, and translate
Japanese messages. Intelligence information gathered from the messages was
sent to military command at the Office of Strategic Services (OSS). The
ability to decipher and read Japanese communications was one of the key
components of the Allied victory in the Pacific.

Even before the outbreak of World War II in Europe in 1939, the United
States began its efforts to decode Japanese diplomatic and military
communications. In 1923, a United States Navy intelligence officer
obtained contraband copy of the World War I era Japanese Imperial Navy
Secret Operating Code. Photographs of the codebook were passed on to the
cryptologists at the Research Desk, where code was placed in red folders
after the additive code keys were fully discovered. The simple additive
code became known as "Red," after the folders in which it
was stored.

For high-level communications, the Japanese replaced Red with Blue, a more
sophisticated code in 1930. However, the new code too closely resembled
its predecessor, allowing United States cryptologists to fully break the
new cipher in less than two years. At the outbreak of World War II, the
Japanese were still using both Red and Blue for various communications.
U.S. military intelligence established listening stations throughout the
Pacific to monitor ship-to-ship, command-to-fleet, and land-based
communications.

After war broke out in Europe, the Japanese received encryption and
security help from Nazi Germany. The Germans had discovered that U.S.
intelligence was monitoring and decoding Japanese communications as early
as 1935, but they did not immediately inform the Japanese. Later, Germany
sent a copy of their infamous Enigma encryption machine, with a few
modifications, to help secure Japanese communications. As a result, U.S.
intelligence could no longer read Japanese intercepts. The painstaking
work of U.S. cryptologists began anew.

U.S. cryptanalysts named the new code Purple. Applied to several
variations of the initial Enigma code, Purple provided the most
significant challenge to both United States and British intelligence
during the war.

With the aid of information from Polish and Swedish cryptologists, the
British military intelligence cryptanalysis unit at Bletchley Park first
broke the German Enigma code. They then developed sophisticated decoding
bombes and the first programmable computer to facilitate the deciphering
of the complex Enigma code. By 1943, British intelligence was able to
utilize almost real-time intelligence information received from translated
Enigma intercepts.

In the United States, cryptologists struggled to break the Purple by hand.
However, the structure of Japanese messages, always beginning with the
same introductory phrase, aided code breakers in determining the
sequencing of the multi-rotored Japanese cipher machine. United States
code breakers had made significant progress on the Purple code by 1941,
gaining the ability to read several lines of intercepts. The process
remained slow, and the information gained from Purple was usually outdated
by the time it was translated.

Aware of British successes against the German Enigma machine, United
States military intelligence asked their ally to share code-breaking
information. The British sent top Bletchley Park cryptographers and
engineers to the United States to help train code breakers and build
decoding bombes. However, they closely guarded, and did not share, the
secret of Enigma code breaking efforts (code named Operation Ultra) that
involved Colossus, the Bletchley Park decoding computer.

With the aid of the British, United States intelligence made significant
progress against Purple in a short time. A replica of the Japanese Purple
machine, built in 1939 by
American cryptologist William Friedman, was used to adapt a German Enigma
bombe to decode Japanese Purple. Although the settings for each message
had to be determined by hand, United States intelligence gained the
ability to read Japanese code with greater ease, in a more timely manner,
by 1942, six months after the Japanese bombing of Pearl Harbor and the
entry of the United States into World War II.

Utilizing their extensive network of listening stations in the Pacific,
United States intelligence intercepted and decoded several other types of
messages. Diplomatic Purple messages, paired with JN-25 intercepts,
another broken Japanese Navy code, gave U.S. military command vital
information about Japanese defenses at Midway. Operation Magic intercepts
provided useful information during the ensuing Battle of Midway, turning
the tide of the war in the Pacific in favor of the allied forces. A year
later, Purple intercepts gave the U.S. information about a diplomatic
flight on which Japanese General Yamamoto, the mastermind behind the Pearl
Harbor attack, was traveling. U.S. planes shot down the Japanese aircraft.

Operation Magic provided critical intelligence information in both the
Pacific and European theaters of war. Diplomatic messages between Berlin
and Tokyo, encoded with Enigma and Purple, yielded British and United
States intelligence information regarding German defenses in France. The
information helped commanders plan the DDay invasion of Normandy in June
1944.

The Japanese government remained unaware that the United States broke the
Purple code. Japanese Imperial forces continued to use codes broken by
Operation Magic throughout the war and in the weeks following the Japanese
surrender in 1945.